Method for channel estimation when using different modulation methods within one signal interval

ABSTRACT

The method is based on a signal interval (DB) which comprises a first part (ET) (which is modulated using a first modulation method (GFSK)) of the signal interval and a second part (which is modulated using a second modulation method (DMPSK)) of the signal interval. The channel parameters (c(i)) relating to the second part (which is modulated using the second modulation method) of the signal interval are determined using a received data signal (a(i); p(i)) from the first part (ET) of the signal interval (DB).

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of co-pending InternationalApplication No. PCT/DE2004/002292 filed Oct. 15, 2004 which designatesthe United States, and claims priority to German application number DE103 48 205.9 filed Oct. 16, 2003.

TECHNICAL FIELD

The invention relates to a method for determination of channelparameters in a mobile radio receiver relating to a second part of asignal interval, with the signal interval comprising a first part whichis modulated using a first modulation method of the signal interval andthe second part which is modulated using a second modulation method ofthe signal interval.

BACKGROUND

At present, in digital cordless communication systems which are based onthe Bluetooth Standard Version 1.1, data is transmitted as standard atrates of 1 Mbit/s. In this case, a two-value GFSK modulation method(Gaussian Frequency Shift Keying) is used. The GFSK modulation method isa frequency-shift keying modulation method (FSK—Frequency Shift Keying).In the case of GFSK-based modulation, a Gaussian filter is also used atthe transmission end, in order to limit the frequency bandwidth. Afilter such as this results in pulse-shaping of the frequency and datapulses, with the pulse per symbol extending over a time of more thanonly the symbol time duration T.

One possible way to achieve higher data transmission rates is to usemodulation methods with more values, such as the four-value DQPSK method(Differential Quadrature Phase Shift Keying) or, in general, the DMPSKmethod, in which an M-value symbol where M≧4 is transmitted instead of atwo-value bit. For future versions of the Bluetooth Standard (possiblyeven from Version 1.2, but at the latest from Version 2.0), it isplanned to increase the data rate using a modulation method with morevalues.

In order to achieve an increase in the data rate in later versions of aStandard for standardized digital radio transmission systems, it isworthwhile changing from a modulation method with a small number ofvalues (for example GFSK) to a modulation method with more values (forexample DQPSK) once the radio link has been in existence for a certaintime. This allows backward compatibility of the new version of theStandard with the earlier versions of the Standard. Setting up aconnection, or setting up a so-called piconetwork in the case of theBluetooth Standard, can in this case first of all be carried out usingthe modulation method with a small number of values as used for all theappliances according to the Standard. If both of the appliances in alink or piconetwork that has been set up are designed for modulationwith more values, this modulation can be used for the subsequent datatransmission. In general, in digital TDMA (Time Division MultipleAccess)-based mobile radio systems, the information is transmitted inthe form of a data burst with a defined time. In the case ofpacket-oriented mobile radio systems, a data packet to be transmittedextends over one or more data bursts. A data burst comprises a firstdata burst header or data packet header. The header contains necessaryinformation for addressing the remote end and for indication of thepacket type, and should thus, for compatibility reasons, be transmittedusing a modulation method with a small number of values, for allversions of the Standard. In particular, it is also feasible for theheader to indicate to the respective remote end that it should switch toa second modulation method, with more values. Switching to a modulationmethod with more values then does not take place until a second part ofthe data burst. If a plurality of data packets are transmittedsuccessively, the modulation method is thus switched alternately aplurality of times. For receiver-end recovery of the data that ismodulated with more values in the second part of a burst, it isfundamentally possible because of the greater disturbance sensitivityinvolved with this to use methods which require channel estimation. Theaim of channel estimation is to indicate channel parameters whichdescribe the transmission behavior of the channel. In this case, thechannel parameters include the influences of the air interface, whichfrequently has frequency selectivity and multipath propagation.Furthermore, it is possible to take account of the influences oftransmission and/or receiving components in the channel estimation.These are frequently dependent on the modulation type being used.Furthermore, the channel parameters are also influenced by temperatureeffects, ageing or component tolerances of the analogue receivingcomponents (front end).

For channel estimation, a received signal in a training sequence isgenerally compared with a reference signal which is known at thereceiver end. The achievable estimation accuracy for channel estimationand thus also the performance of the receiver are generally increasedwith the number of known data elements.

Future versions of the Bluetooth Standard will provide a trainingsequence for channel estimation in the second part of a data burst,which is modulated with more values. However, the number of symbols inthis training sequence is relatively small, so that the achievableestimation accuracy of the channel parameters determined on the basis ofthis training sequence may be inadequate.

SUMMARY

The invention is thus based on the object of specifying a method whichworks sufficiently accurately for determination of channel parameterswhich, once a modulation change has occurred within a signal interval,relate to a second part of the signal interval, which is modulated usinga second modulation method.

The method according to the invention is in this case based on a signalinterval comprising a first part (which is modulated using a firstmodulation method) of the signal interval and a second part (which ismodulated using a second modulation method) of the signal interval. Thechannel parameters relating to the second part (which is modulated usingthe second modulation method) of the signal interval are determined,according to the invention, using a received data signal from the firstpart of the signal interval.

As is generally known, methods for channel estimation fundamentallyoperate with receiver-end reference data, which is compared with thereceived signal. The reference signal which is associated with thereceived data signal may represent data information which is alreadyknown in the receiver, in particular stored data information, or elseinformation which is obtained by processing of the received signal. Ifreference information is determined without data information being knownat the receiver end, then this is also referred to as so-called blindestimation or blind equalization. In this case, the reference signal isgenerally determined by means of detection (decision-directed) of thereceived signal.

The method according to the invention offers the advantage that it ispossible to use a greater amount of reference data for the estimationmethod. Thus, in addition to the reference data in the second part ofthe signal interval, it is also possible to use reference data in thefirst part of the signal, and correlate this with the correspondingreceived signal. With the increase in the number of reference dataitems, the estimation accuracy for the channel parameters to beestimated increases. Furthermore, when exclusive use is made of areceived data signal from the first signal interval for channelestimation, the method according to the invention makes it possible toprovide the channel parameters at an earlier time so that they can beused earlier for data recovery than is the case when exclusively using atraining sequence from the second part of the signal interval.

For the purposes of this application, channel parameters are not in thiscase understood as meaning only channel parameters in the relativelynarrow sense, that is to say as parameters of a transfer function orimpulse response to be estimated, and as the transfer function orimpulse response itself, but also in the wider sense as parameters of asignal equalizer or input filter (matched filter). Since the object ofsuch receiving components is to compensate for channel influences in thereceived signal, their parameters can in principle be determined fromthe channel parameters in the narrower sense, that is to say the impulseresponse of the channel.

Furthermore, the channel parameters can describe not only the essentialinfluences of the air interface but also, optionally, the influences ofone or more transmitting and/or receiving components.

The signal interval, which comprises a first part (which is modulatedusing a first modulation method) of the signal interval and a secondpart (which is modulated using a second modulation method) of the signalinterval, advantageously corresponds to a data burst. In relativelyrecent versions of packet-oriented mobile radio standards, it ispossible to modulate the information of a first header or access codefor addressing and control of the remote end using the first modulationmethod, so that it is obtained in a form which is recoverable even bythose receivers which are based on earlier versions of the Standard. Amethod which is used for such a data burst for determination of thechannel parameters of the second part of the data burst offers theadvantage that the channel parameters estimated in this way differ onlyslightly from the actual channel relationships, because of the shorttime difference between the occurrence of the data signal (first part ofthe burst) which determines the estimation and the time of use (secondpart of the burst) of the estimated channel parameters. If the timeinterval were longer, the discrepancies would also be greater, since thechannel relationships vary continuously, especially in the case ofchannels with fast fading.

According to one advantageous embodiment, channel parameters relating tothe first part of the data burst are determined first of all in a firststep using a received data signal from the first part of the data burst.This is based on the assumption that these channel parameters which aredetermined in the first step describe only the modulation-independentpart of the channel.

This measure makes it possible for the channel parameters which aredetermined in the subsequent step and relate to the second part of thedata burst to be determined in a simple manner from the channelparameters relating to the first part. If the channel parameters to beestimated relating to the second part of the data burst do not comprisethe modulation-dependent components, then the sets of channel parameterscorrespond to one another. If the channel parameters to be estimated inthe second part also describe the modulation-dependent components, thechannel parameters to be estimated in the second part of the data burstcan be determined by means of a simple convolution operation. For thispurpose, the channel parameters determined in the first step areconvolved with the impulse response of the modulation-dependentcomponents of the second modulation method. It is advantageouslypossible to provide for the first part of the data burst to comprise anaccess code and a first header, and for the second part of the databurst to comprise a training sequence. This offers the capability toalso use information in the form of a training sequence from the secondpart of the data burst, in addition to the information from the firstpart that is known at the receiver end, in order to estimate the channelparameters.

According to a first advantageous embodiment, the channel parametersrelating to the first part of the data burst are estimated with the aidof an MMSE (Minimum Mean Square Error) estimation method, in particularwith the aid of an MAP-LMMSE (MAP—Maximum a-Posteriori; LMMSE—LinearMinimum Mean Square Error) estimation method, using the received datasignal from the reference information which is associated with the firstpart of the data burst and with this data signal. The data signal whichis used may also in particular represent the access code or a part ofthe access code. In this case, it is advantageous for the referenceinformation and/or as a function of this, a plurality of results of thecomputation operations of the MMSE and LMMSE estimation method to be orstored in the receiver in the factory.

The MMSE and LMMSE methods which are known to those skilled in the artare based on minimizing the mean square estimated error. The genericexpression an MMSE estimator covers not only ML (maximum likelihood)estimators but also MAP estimators, in which case, in contrast to MLestimators, MAP estimators use so-called a-posteriori information, thatis to say information which is known in advance, for example about thechannel noise or the channel as such. In contrast to the MMSE method, alinear estimator is an essential precondition for the LMMSE method.Matrix operations, in particular matrix inversions and matrixmultiplications, are carried out in MMSE or LMMSE methods for estimationof the channel parameters. One of the basic matrices is theautocorrelation matrix, whose elements are dependent on a standardizeddata sequence. In addition to the reference sequence, theautocorrelation matrix also represents reference information that isknown at the receiver end, for the purposes of the invention. In orderto reduce the computation complexity, the result of the matrix inversionof the autocorrelation matrix, the standardized data sequence or resultsof other computation operations which are dependent thereon may, forexample, be stored in the channel estimator at this stage.

According to an alternative embodiment to this, the channel parametersrelating to the first part of the data burst are estimated with the aidof an iterative LMS (Least Mean Square) estimation method, using thereceived data signal from the first part of the data burst and referenceinformation which is associated with this data signal.

In principle, this offers the advantage that the estimation of thechannel parameters can be carried out without matrix inversion. Since,for example, the information of the access code which can be used in theestimation method is normally available, in particular in the case ofBluetooth systems, only when the connection is set up, a matrixinversion of the autocorrelation matrix would have to be carried outduring operation for non-iterative estimation methods. The channelparameters can be determined without matrix inversion with the aid ofthe iterative LMS method, which is known to those skilled in the art.Furthermore, iterative estimation methods such as the LMS method requireconsiderably more reference information in order to achieve adequateestimation accuracy. The use of the bit sequence of the access code,which is longer than the header, is thus particularly suitable for useof the LMS method.

It is advantageously possible to provide for a modulation-dependentreference signal first of all to be determined as reference informationfor estimation of the channel parameters relating to the first part ofthe data burst. The modulation-dependent reference signal is in thiscase determined by pulse-shaping corresponding to the first modulationmethod of a modulation-independent reference sequence.

In principle, as mentioned above, the channel parameters can describenot only the essential influences of the air interface but also,optionally, influences of one or more transmitting and/or receivingcomponents. Of the optional influences, transmission-end pulse-shapingwhich is dependent on the modulation method should be mentioned inparticular. In order to determine the channel parameters relating to thesecond part (which is modulated using the second modulation method) ofthe data burst, the channel parameters relating to the first part (whichis modulated using the first modulation method) of the data burst arefirst determined. In this case, these initially determined channelparameters describe only the modulation-independent part of the channel.The above procedure makes it possible to directly calculate the channelparameters relating to the first part without the influence of themodulation, that is to say without the influence of themodulation-dependent pulse-shaping. In this case, amodulation-independent reference sequence, that is to say adiscrete-value symbol sequence, is converted to a modulation-dependentreference sequence, that is to say to a pulse-modulated symbol sequence.There is therefore no need to calculate the modulation-dependent part ofthe channel parameters from the channel parameters relating to the firstpart.

According to a further advantageous embodiment, additional channelparameters relating to the second part (which is modulated using thesecond modulation method) of the data burst are, furthermore, determinedusing a received data signal from the training sequence and referenceinformation which is associated with this data signal. In this case, itis advantageous for the channel parameters relating to the second partof the data burst to be determined using the additional channelparameters.

A procedure such as this makes it possible to further improve theaccuracy of the channel estimate. In a case such as this, the channelestimate is not just dependent on the first part of the data burst.

In this case, the channel parameters relating to the second part of thedata burst are preferably determined as a function of a selectionvariable, which is dependent on the respective connection,

-   a) as resultant channel parameters relating to the first part of the    data burst which are obtained from the transmission-end    pulse-shaping using the second modulation method of the determined    channel parameters relating to the first part of the data burst, or-   b) as additional channel parameters relating to the second part of    the data burst, with these channel parameters taking account of the    transmission-end pulse-shaping in the second modulation method, or-   c) as averaging of the individual resultant channel parameters and    of the individual additional channel parameters, in which case these    take account of the transmission-end pulse-shaping in the second    modulation method.

This offers the advantage that the channel estimate can be flexiblymatched to different transmission conditions. It is known that thequality of the channel estimators a) and b) is dependent on thetransmission conditions. If the estimate a) based on the first part ofthe data burst is better, then this is used exclusively for indicationof the channel parameters.

If, in contrast, the estimate b) based on the second part of the databurst is better, then only these results are used for channelestimation. If the quality of the two estimators a) and b) iscomparable, then the quality of the estimate can be improved further byaveraging the results of the two estimators.

According to one advantageous embodiment, the first modulation methoddescribes GFSK modulation, and the second modulation method describesDMPSK modulation where M≧4. In this case, the modulation index of theGFSK modulation is advantageously determined, and then represents theselection variable which is dependent on the respective connection.

This extension to the method takes account of the influence of themodulation index of the GFSK modulation on the quality of the channelestimate relating to the second part of the data burst. This thereforemakes it possible to determine the channel parameters to be estimatedfor the second part of the data burst optimally and sufficientlyaccurately despite the modulation index having a particularly poorvalue.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail in the following textusing one exemplary embodiment and with reference to the drawings, inwhich:

FIG. 1 shows an illustration of the structure of a data burst;

FIG. 2 shows an illustration of the impulse response c(i) of thechannel;

FIG. 3 a shows an illustration of one implementation of the estimationof channel parameters c_(GFSK)(i) relating to the first part of the databurst with the aid of the LMMSE method;

FIG. 3 b shows an illustration of an alternative implementation of theestimation of channel parameters c_(GFSK)(i) relating to the first partof the data burst with the aid of the LMS method; and

FIG. 4 shows an illustration of the determination of the channelparameters c(i) as a function of the modulation index η.

DETAILED DESCRIPTION

FIG. 1 shows a structure of a data burst DB interchanged between thesubscribers in an already set-up piconetwork by radio in a Bluetoothtransmission system based on a Bluetooth Standard higher than 1.1.

The data burst DB or the data packet in FIG. 1 comprises a first partET, which has an access code AC arranged at the start with the symbolsequence {a(1), a(2), . . . , a(N_(a)−1), a(N_(a))} and a first headerH1 following this with the symbol sequence {p(1), p(2), . . . ,p(N_(H1)−1), p(N_(H1))}. A guard time interval SZI is optionallyadjacent the header H1 of the first part ET. The data burst DBfurthermore comprises a second part ZT, which follows the guard timeinterval SZI. The second part ZT has a second data burst header or asecond header H2, followed by a training sequence Sync2 with the symbolsequence {q(1), q(2), . . . , q(N_(S2)−1), . . . q(N_(S2))}. Thistraining sequence is followed by the payload data area P of the secondpart ZT.

At the start of the transmission of the data packet or data burst DB,the first part ET which is modulated using a two-value GFSK modulationmethod is transmitted at a first data rate by the transmitting radiounit, and is received by a remote station. The first data rate, as theBluetooth Standard data rate, is 1 Mbit/s. On a standard-specific basis,identification and synchronization information is transmitted at thestart of the first part ET by means of the access code AC of thepiconetwork, followed by the first data burst header H1. The access codeis known once the piconetwork has been set up. The header H1, as afurther component of the first part of the burst, may include not onlyaddressing information and details relating to the packet type used butalso information about a second data rate at which the second part ZT ofthe data burst DB, which follows the first part ET, is intended to betransmitted. The second part ZT is transmitted at a higher data ratethan the first part ET. In the exemplary embodiment, the second part ZTof the data burst DB is transmitted using a second modulation method,which is based on DMPSK modulation where M≧4. In the case of DQPSKmodulation with four-value symbols, the second part ZT of the burst istransmitted at twice the data rate of a transmission based on GFSKmodulation. No data is transmitted during the optional time period ofthe guard time interval SZI. The guard time interval SZI is used formodulation-dependent component switching at the transmission andreception ends.

If both appliances in the radio link support the increased data ratebased on DMPSK modulation, switching from the first modulation method tothe second modulation method can take place in each burst. In this case,the check for support of the increased data rate is actually carried outwhile the piconetwork is being set up.

For reception-end recovery of the data (payload) which is contained inthe second part of the data burst DB, it is generally necessary to knowthe transmission response of the channel for DMPSK modulation. In thiscase, in particular, the transmission-end pulse-shaping, which isselected depending on the modulation method, has a different effect onthe transmission response of the overall channel—comprising the airinterface, transmitter and receiver.

The modulation-dependent pulse-shaping can be characterized by a linearpulse g_(Modulation)(i). In the case of Gaussian pulse-shaping, thepulse extends over a time of more than just the symbol time duration T.As part of the channel, the air interface generally has the response ofa multipath channel, that is to say the transmitted signal reaches thereceiver via a plurality of paths delayed in time with respect to oneanother. The transmission response of a multipath channel such as thiscan be characterized by its impulse response c_(MP)(i). In this case,the impulse response c_(MP)(i) can describe not only the air interfacebut also further parts of the channel, in particular the receptionfilters.

The impulse response of the resultant channel which comprises both themultipath channel and the transmission-end pulse-shaping is given by:c(i)=g _(Modulation)(i)*c _(MP)(i)  (1).

FIG. 2 shows an example of the profile of the impulse response of theresultant channel with L=3 coefficients. In this case, the channel isdescribed by a model with three coefficients, wherec _(i) =c(i) where i=−1, 0, 1  (2).The received signal r(i) is given by

$\begin{matrix}{{{r(i)} = {{{{s(i)}*{c(i)}} + {n(i)}} = {{\sum\limits_{k = {{- {({L - 1})}}/2}}^{{({L - 1})}/2}{{s\left( {i - k} \right)} \cdot {c(k)}}} + {n(i)}}}},} & (3)\end{matrix}$where s(i) denotes the transmitted signal, n(i) the noise signal with anoise power P_(noise) and “*” the convolution operator.

The most obvious approach for estimation of the channel parameters c(i)relating to the second part of the burst is to use the known trainingdata q(1), q(2), . . . , q(N_(S2)−1), Q(N_(S2)) in the sequence Sync2 ofthe second part ZT of the burst for channel estimation. However, thenumber of these training data items is relatively small. For thisreason, it is not possible to achieve very good accuracy with a channelestimation process such as this, which is based solely on the abovetraining data as reference information that is known at the receivingend.

According to the invention, the channel parameters c(i) relating to thatpart of the data burst DB which is modulated using DMPSK are determinedusing the received data from the first part of the burst. For thispurpose, in this exemplary embodiment, the channel parameters c_(MP)_(—) _(GFSK)(i) relating to the first part ET are determined first ofall, in which case these channel parameters describe only themodulation-independent part of the channel.

FIG. 3 a shows one implementation of the estimation of the channelparameters c_(MP) _(—) _(GFSK)(i) relating to the first part with theaid of the LMMSE (Linear Minimum Mean Square Error) method based onminimizing the mean square estimation error. The received data signalr(i) from one part of the access code AC and the reference sequence a(i)associated with this data signal are used as input variables forestimation. Furthermore, the pulse g_(GFSK)(i) which describes thepulse-shaping must be known in order to estimate c_(MP) _(—) _(GFSK)(i).Furthermore, the estimate can optionally be improved by inclusion of themeasured noise power P_(noise).

Chapters 5.2.2 and 5.2.3, pages 197 to 206, of the textbook Analyse undEntwurf digitaler Mobilfunksysteme, P. Jung, Teubner-Verlag, 1997[Analysis and design of digital mobile radio systems] describe thecomputation steps for determination of the channel impulse response.These details are hereby incorporated by reference in the disclosurecontent of this document.

In general, the vector of the coefficients of a sought impulse responsec can be determined to be:c =(c− _((L−1)/2) . . . c ₀ . . . c _((L−1)/2))^(T) =M·r   (4),where M describes the estimation matrix and r=(r_(a(min))r_(a(min+1)) .. . r_(a(max)))^(T) describes the vector of the received signal withrespect to a reference sequence a(i). In this case, only one part of theaccess code is considered.

One requirement of an MMSE estimator is that the square of the estimatederror is a minimum. One suitable possible estimation matrix may bedefined on the basis of this requirement as:M =( R ⁻¹ ·P )^(*T)  (5),where R describes the autocorrelation matrix of the received trainingsequence and P describes the cross-correlation matrix between thereceived training sequence and the impulse response of the channel. Theautocorrelation matrix R is a function of the training sequence beingused, of the channel noise and of the correlation characteristics of theimpulse response to be estimated. In the definition of theautocorrelation matrix R the channel noise and the correlationcharacteristics of the impulse response to be estimated are used onlyoptionally in order to improve the estimate. This optional informationrepresents a-priori estimation information. The use of a-prioriestimation information therefore represents an MAP estimator, inparticular an MAP-LMMSE estimator as a result of the use of a linearestimator. The cross-correlation matrix P is a function of the trainingsequence and of the correlation characteristics of the impulse responseto be estimated.

In the case of the estimator illustrated in FIG. 3 a, resultantreference information p_(res)(i) in the formp _(res)(i)=g _(GFSK)(i)*a(i)  (6)is used as reference information. This offers the advantage that thechannel estimate as shown in FIG. 3 a does not define the channelparameters for the channel including GFSK pulse-shaping, but only thechannel parameters c_(MP) _(—) _(GFSK)(i) without GFSK pulse-shaping.The estimation matrix, the autocorrelation matrix and thecross-correlation matrix are in this case determined analogously toequation (5). Instead of using a convolution operation, the same resultcan also be obtained by filtering as appropriate for the convolution.This applies in principle to all convolution operations cited in thisapplication.

Sequence {a(min), . . . , a(max)} is a sub-sequence of the access code,which comprises 68 bits, and is known once a connection has been set upin a Bluetooth-specific piconetwork. A synchronization sequence with alength of 64 bits is determined as part of the access code as a functionof the so-called network-specific LAP address, and is described inSection 13.2.1, pages 142 to 145 of the Bluetooth Specification 1.1. Inthis case, depending on the value of one specific bit in the LAPaddress, the synchronization sequence has a first or a secondStandard-specific bit sequence, with a length of 6 bits, at the end ofthe synchronization sequence. Furthermore, depending on the same bits inthe LAP address, a first or a second Standard-specific bit sequence witha length of 4 bits is defined at the end of the access code, theso-called trailer bits. The sequence {a(min), . . . , a(max)} which isused for MAP-LMMSE estimation corresponds to the cohesive sequence of 11bits of the access code which results from this, with two permutationsof the sequence {a(min), . . . , a(max)} being possible depending on thevalue of the specific bit in the LAP address. The two permutations ofboth the inverted autocorrelation matrices R and cross-correlationmatrices P which correspond to the sequence, or the two estimationmatrices M, directly, can be stored in the memory in the receiver at thefactory. In this case, a specific value is assumed for the noise powerP_(noise), and corresponds to the minimum value to be expected of thenoise power P_(noise). Furthermore, it is also possible to store otherresults calculated in advance. Depending on which permutation of thereference sequence actually occurs, one of the two invertedautocorrelation matrices R and one of the two cross-correlation matricesP or estimation matrices M in each case are selected for estimation.

FIG. 3 b shows an alternative implementation of the estimation of thechannel parameters c_(MP) _(—) _(GFSK)(i) relating to the first partwith the aid of the iterative LMS (Least Mean Square) method based onminimizing the mean square estimation error. The received data signalr(i) from the entire access code AC and the reference information a(i)associated with this data signal are used as input variables forestimation. Furthermore, it is necessary to know the pulse g_(GFSK)(i)which describes the pulse-shaping in order to estimate c_(MP) _(—)_(GFSK)(i).

In this case, analogously to the MAP-LMMSE estimator, the resultantreference information a_(res)(i) based ona _(res)(i)=g _(GFSK)(i)*a(i)  (7)is used as reference information for the LMS channel estimate.

The entire sequence of the access code a(i) is known once thepiconetwork has been set up. Since the number of permutations of areference sequence based on the entire access code is very large, all ofthe computation operations in the estimation process must also becarried out in the receiver without being able to access previouslycalculated values.

As already mentioned, only a part of the access code with a size of 11bits can be used for the MAP-LMMSE estimate when it is intended to usestored values for the matrices used for the estimation method.

The known iterative LMS method may, however, be used to estimate thechannel parameters without matrix inversion, so that the entire accesscode AC can be used as reference information for the estimation method,with little computation complexity. In this case, of course, it wouldalso be feasible to use only a part of the entire access code forestimation. In the LMS method, as in the case of the MAP-LMMSEestimation method, the square of the error is minimized. The LMS methodoperates on the basis of an iterative gradient method (method of thesteepest descent), with the minimum square error being reached after atotal number n of iterations. The associated channel parameters thencorrespond to the estimation result. The LMS method is described indetail in Chapter 11.1.2, pages 663 to 666 of the textbook DigitalCommunications, J. G. Proakis, Fourth Edition, McGraw-Hill and is herebyincluded by reference in the disclosure content of this document.

Additional channel parameters c_(DMPSK)(i) relating to theDMPSK-modulated second part ZT of the data burst can optionally bedetermined in addition to the estimation of the channel parametersc_(MP) _(—) _(GFSK)(i) relating to the GFSK-modulated first part on thebasis of the alternative embodiments shown in FIG. 3 a or FIG. 3 b. Inthis case, the additional channel parameters c_(DMPSK)(i) are determinedusing a received data signal from the training sequence Sync2 in thesecond part of the burst, and a reference sequence q(i) which isassociated with this data signal. This reference sequence has a lengthof 10 training symbols in the case of the Bluetooth Standard. With DQPSKmodulation, this corresponds to a length of 20 bits. Since the entireestimation method has the aim of determination of the channel parametersc(i) relating to the DMPSK-modulated part including the DMPSK-specifictransmission-end pulse-shaping, it is worthwhile for the additionalchannel parameters c_(DMPSK)(i) to also describe the DMPSK-specificpulse-shaping of the transmission end. The additional channel parametersc_(DMPSK)(i) can be determined using an LMMSE or LMS methodcorresponding to that shown in FIG. 3 a or 3 b, respectively. In thiscase, however, there is no need to produce a resultant reference signalby means of the convolution operation; the reference sequence {q(1) . .. q(N)} in this case forms the input signal for the LMMSE or LMSoperation.

FIG. 4 illustrates the determination of the channel parameters c(i) fromthe previously described estimation results c_(MP) _(—) _(GFSK)(i) andc_(DMPSK)(i). The channel parameters c_(MP) _(—) _(GFSK)(i) relating tothe GFSK-modulated first part of the data burst, which were determinedusing one of the methods illustrated in FIG. 3 a or FIG. 3 b, are firstof all convolved with the pulse g_(DMPSK)(i) of the pulse-shaping usedfor the DMPSK modulation. In contrast to the pulse of the GFSKmodulation, this pulse is a so-called Nyquist pulse. The convolutionresult c_(MP) _(—) _(GFSK) _(—) _(PF) _(—) _(DMPSK)(i) forms a selectionoption of a subsequent 3-to-1 selection operation S for indication ofthe sought channel parameters c(i). Furthermore, the additional channelparameters c_(DMPSK)(i) relating to the DMPSK-modulated second part ZTrepresent a further selection option. The third selection option isobtained as an average M of the channel responses c_(MP) _(—) _(GFSK)_(—) _(PF) _(—) _(DMPSK)(i) and c_(DMPSK)(i). In this case, the 3-to-1selection S is controlled via the modulation index η, which is known bymeasurement.

The reason for choice of channel estimation for indication of the soughtestimation result is that the quality of the channel parameters c_(MP)_(—) _(GFSK)(i) based on the first part ET of the data burst isdependent on the modulation index η of the GFSK modulation for therespective connection. The modulation index may fluctuate within acertain tolerance interval. It is known that estimation based on theGFSK-modulated part may become very poor for certain values of themodulation index. This is because the correlation characteristics of therespectively used resultant reference sequence change as a function ofη. In a situation such as this, only the channel parameters c_(CMPSK)(i)are used for indication of the sought channel parameters c(i). Forcertain other values of the modulation index η, the estimation accuracybased on the first part of the data burst is very good, so that, in thiscase, an appropriate choice allows the channel parameters c_(MP) _(—)_(GFSK,PF) _(—) _(DMPSK)(i) to be equated to the sought channelparameters c(i). If the accuracy of the channel parameters c_(CMPSK)(i)and c_(MP) _(—) _(GFSK,PF) _(—) _(DMPSK)(i) is comparable, averaging Mof the parameter sets can be carried out. This measure results in theaveraged estimation result having a narrower fluctuation width than theindividual parameter sets so that, on average, the sought estimationresult c(i) is more accurate.

Finally, it should be noted that it is also possible within the scope ofthe invention to take account in the determination of the channelparameters of changes in the transmission characteristic of thereception signal path in the receiver front end, which occur whenswitching between the various modulation methods, owing to the use ofdifferent receiver modules in the reception signal path. If therespective transmission characteristics of the reception signal path inthe receiver front end are known, these can be used in an analogousmanner to the modulation-dependent pulse-shaping for calculation of thechannel parameters relating to the second part which is modulated usingthe DMPSK modulation method of the data burst.

What is claimed is:
 1. A method for determination of channel parametersin a mobile radio receiver relating to a second part of a signalinterval, with the signal interval comprising a first part which ismodulated using a first modulation method and a second part which ismodulated using a second modulation method, with the first part and thesecond part being filtered using different pulse shapes, the methodcomprising: estimating channel parameters relating to the first part ofthe signal interval from the first part of the signal interval, anddetermining the channel parameters relating to the second part of thesignal interval from the channel parameters relating to the first partof the signal interval, further comprising: applying the pulse-shape ofthe first part of the signal interval to determine the channelparameters relating to the second part of the signal intervalindependent of the modulation-dependent pulse shaping of the first part,and using the pulse-shape of the second part of the signal interval todetermine the channel parameters relating to the second part of thesignal interval from the channel parameters relating to the first partof the signal interval.
 2. The method according to claim 1, wherein thesignal interval corresponds to a data burst.
 3. The method according toclaim 2, wherein the first part of the data burst comprises an accesscode and a first header, and the second part of the data burst comprisesa training sequence.
 4. The method according to claim 3, wherein thechannel parameters relating to the first part of the data burst areestimated by a MMSE estimation method using the received data signalfrom the first part of the data burst and reference information which isassociated with this data signal.
 5. The method according to claim 3,wherein the channel parameters relating to the first part of the databurst are estimated by a MAP-LMMSE estimation method using the receiveddata signal from the first part of the data burst and referenceinformation which is associated with this data signal.
 6. The methodaccording to claim 4, wherein the reference information and/or,depending on this, a plurality of results of the computation operationsof the MMSE estimation method are stored in the receiver at a factory.7. The method according to claim 5, wherein the reference informationand/or, depending on this, a plurality of results of the computationoperations of the LMMSE estimation method are stored in the receiver ata factory.
 8. The method according to claim 3, wherein the channelparameters relating to the first part of the data burst are estimatedwith the aid of an iterative LMS estimation method using the receiveddata signal from the first part of the data burst and referenceinformation which is associated with this data signal.
 9. The methodaccording to claim 4, further comprising: determining amodulation-dependent reference signal as reference information bypulse-shaping of a modulation-independent reference sequence using thefirst modulation method.
 10. The method according to claim 3, furthercomprising: determining additional channel parameters relating to thesecond part of the data burst which is modulated using the secondmodulation method from the training sequence of the received data signaland reference information which is associated with this data signal. 11.The method according to claim 10, wherein the determination of thechannel parameters relating to the second part of the data burst iscarried out using the additional channel parameters.
 12. The methodaccording to claim 11, wherein the channel parameters relating to thesecond part of the data burst are determined as a function of aselection variable, which is dependent on the respective connection, asresultant channel parameters relating to the first part of the databurst which are obtained from a transmission-end pulse-shaping using thesecond modulation method of the determined channel parameters relatingto the first part of the data burst, or as additional channel parametersrelating to the second part of the data burst, with these additionalchannel parameters taking account of the transmission-end pulse-shapingin the second modulation method, or as averaging of the individualresultant channel parameters and of the individual additional channelparameters, in which case these take account of the transmission-endpulse-shaping in the second modulation method.
 13. The method accordingto claim 1, wherein the first modulation method is GFSK modulation, andthe second modulation method is DMPSK modulation with M≧4.
 14. Themethod according to claim 12, wherein the method comprises:determination of a modulation index of a GFSK modulation, wherein theselection variable is the modulation index.
 15. The method according toclaim 1, wherein the method is used in a Bluetooth transmission systembased on a Bluetooth Standard Version 1.2 or higher.
 16. A method fordetermination of channel parameters in a mobile radio receiver relatingto a second part of a data burst, with the data burst comprising a firstpart which is modulated using a first modulation method and a secondpart which is modulated using a second modulation method, the methodcomprising: determining a modulation-dependent reference signal bypulse-shaping of a modulation-independent reference sequence using thefirst modulation method, determining channel parameters relating to thefirst part of the data burst from the received data signal of the firstpart of the data burst and from the modulation-dependent referencesignal, with these channel parameters describing only themodulation-independent part of the channel, and determining the channelparameters relating to the second part of the data burst from thechannel parameters relating to the first part of the data burst and fromthe pulse shape of the second part of the signal interval.
 17. Themethod according to claim 16, wherein the first part of the data burstcomprises an access code and a first header, and the second part of thedata burst comprises a training sequence.
 18. The method according toclaim 17, wherein the channel parameters relating to the first part ofthe data burst are estimated with the aid of an MMSE estimation methodusing the received data signal from the first part of the data burst andreference information which is associated with this data signal.
 19. Amethod for determination of channel parameters in a mobile radioreceiver relating to a second part of a signal interval, with the signalinterval having a first part which is modulated using a first modulationmethod of the signal interval and a second part which is modulated usinga second modulation method of the signal interval, the methodcomprising: estimating channel parameters relating to the first part ofthe signal interval from the first part and by applying the pulse-shapeof the first part so that the estimated channel parameters relating tothe first part of the signal interval only describe themodulation-independent part of the channel, and estimating the channelparameters relating to the second part of the signal interval which ismodulated using the second modulation method from the estimated channelparameters relating to the first part of the signal interval and byusing the modulation-dependent pulse-shape of the second part of thesignal interval.
 20. The method according to claim 1, wherein thechannel parameters relating to the second part of the signal intervalalso describe the modulation-dependent part of the channel.
 21. Themethod according to claim 19, wherein estimating the channel parametersrelating to the first part of the signal interval comprises convolutingor filtering a modulation-independent reference sequence associated withthe first part of the signal interval by a pulse shape of the firstmodulation method to generate a modulation-dependent reference signal,and estimating the channel parameters relating to the first part of thesignal interval from the first part and the modulation-dependentreference signal.
 22. The method according to claim 19, whereinestimating the channel parameters relating to the second part of thesignal interval comprises convoluting or filtering the channelparameters relating to the first part of the signal interval by a pulseshape of the second modulation method.